The present invention relates to refrigerator apparatus, and more particularly to a cryogenic cooler apparatus in which regeneration and contact between sources of hot and cold are improved to facilitate cooling to temperatures in the range of 3.degree.-4.degree. K.
The proliferation of products utilizing infrared detectors and similar heat-sensitive instruments has dramatically increased the need for cryogenic cooler apparatus. Furthermore, superconducting circuitry and hi-field strength superconducting magnets also require cryogenic cooler apparatus.
Many refrigeration systems utilizing Stirling cycle apparatus and Vuilleumier cycle apparatus have heretofore been developed for cryogenic cooling. In general, these cycles may be described as comprising the steps of supplying fluid such as helium under high pressure, initially cooling the fluid by passing it through regenerators while maintaining the high pressure, and then finally further cooling the initially cooled fluid through expansion and discharge. Typically, such apparatus incorporate pistons or displacers which are reciprocated in cylinders to force the fluid back and forth through regenerators in the appropriate phase relationship to produce cooling. Many of these apparatus have utilized multiple stages.
In cryogenic applications such as those described above, it is generally desirable to cool a medium to a temperature very close to absolute zero. For example, this will maximize sensitivity in a detector or minimize electrical resistance in a conductor. Prior cryogenic cooler apparatus of the Stirling cycle type or of the Vuilleumier cycle type are generally capable of cooling to temperatures in the range of 10.degree.-15.degree. K. In order to produce temperatures in the range of 4.degree.-10.degree. K., it is common to pre-cool helium in a mechanical refrigerator of the aforementioned type. The helium is then passed through a counter-current heat exchanger and finally through a Joule-Thomson expansion valve. The evolving cold gases or vapors pass back up through the heat exchanger, respectively pre-cooling the higher pressure gas before it is throttled. The aforementioned system which utilizes heat exchangers and unidirectional flow is complex, expensive, and susceptible to failures such as plugging due to freezing impurities.
Representative of the U.S. patents relating to cryogenic cooler apparatus are U.S. Pat. Nos. 3,218,815; 3,321,926; 3,372,554; 3,530,681; 3,678,992; 3,717,004; 3,765,187; 3,794,110; 3,991,586; 4,019,336; 4,044,567; 4,078,389; and 4,090,859. The aforementioned U.S. Pat. No. 3,218,815 discloses various cryogenic color apparatus including multiple displacers with internal regenerators. The heat exchange flow path extends through the regenerators and through narrow annular passages between the displacers and the cylinder walls. The aforementioned U.S. Pat. No. 3,794,110 discloses the utilization of .sup.3 He and .sup.4 He or a mixture of the same in heat exchangers in dilution refrigeration systems designed for cooling to temperatures below 10.degree. K.
Also of general interest in this field are the following articles: "The Stirling Refrigeration Cycle" by J. W. L. Kohler published in Scientific American magazine, "Miniature single-stage cryogenerator reaches 30 deg K." by Bernard Kovit published in the January, 1961 issue of Space/Aeronautics magazine, and "Timed surge chamber creates self-acting cryogenic cooler" published in the Oct. 12, 1970 issue of Produce Engineering magazine.